Systems and methods for communicating using ask or qam with uneven symbol constellation

ABSTRACT

Systems and methods of performing ASK or QAM modulation with uneven distance between symbols are provided. Different bit positions mapped to such symbols are assigned to different receivers, with the result that there are different BER performances among bits sent from a transmitter to the different receivers.

FIELD OF THE APPLICATION

The application relates to systems and methods for communicating usingASK (amplitude-shift keying) or QAM (quadrature-amplitude modulation).

BACKGROUND OF THE APPLICATION

Both M-ary amplitude-shift keying (ASK) and M-ary quadrature-amplitudemodulation (QAM) have been widely used in digital communications, whereM is the signal constellation size. In digital modulation with an M-aryconstellation, each block of k=log₂M bits are mapped into an M-arysymbol, where k is a positive integer. The signal constellation,consisting of M points, is a geometric presentation of the candidatebaseband signals to transmit. The M points are distributed on a realaxis for ASK or on a complex plane for QAM to represent the M possiblereal or complex symbols, respectively. In an existing regular ASK or QAMconstellation, the M signal points are evenly distributed, that is, thedistance between any two neighboring signal points of the constellationis equal. The average bit-error rate (BER) performances, that is, therelationship of BER vs. the signal-to-noise ratio (SNR), of differentbits among the k bits are quite similar.

In the application of digital speech communications, the output bitsproduced by a speech codec are typically reordered into a sequence ofdescending importance. The most important bits are those that will havethe greatest impact upon the received voice quality if they are receivedin error. Errors to the least significant bits will have only anegligible impact upon the received voice quality. An example of thismay be found with the AMR codec used in UMTS cellular systems. See 3GPPTS26.101 section 4.2.1 hereby incorporated by reference in its entirety.

It is therefore usual practice to provide additional error protection tothe most important bits. The bits are therefore classed into groups. Thefirst class of bits will receive the greatest protection. The secondclass will receive relatively less protection, and so on for howevermany classes of bits there are. An example of this may be found with theAMR codecs used in UMTS cellular systems. See 3GPP TS26.101 section4.2.2, hereby incorporated by reference in its entirety. In thatexample, the importance classes are Class A, Class B, and Class C. ClassA contains the bits most sensitive to errors and any error in these bitstypically results in a corrupted speech frame which should not bedecoded without applying appropriate error concealment. This class isprotected by the Codec CRC in AMR Auxiliary Information. Classes B and Ccontain bits where increasing error rates gradually reduce the speechquality, but decoding of an erroneous speech frame is usually possiblewithout annoying artifacts. Class B bits are more sensitive to errorsthan Class C bits. The importance ordering applies also within the threedifferent classes and there are no significant step-wise changes insubjective importance between neighboring bits at the class borders.

In another example, when the AMR codec is used with a GSM full ratechannel, the sequencing and classification of bits from speech codecs isgiven in TS 45.003 in section 3.9.4., hereby incorporated by referencein its entirety. The protection classes are: 1a—Data protected with theCRC and the convolution code; and 1b—Data protected with the convolutioncode. No unprotected bits are used.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the application will now be described with reference tothe attached drawings in which:

FIG. 1 is a block diagram of a UASK (amplitude-shift keying with unevenconstellation)/UQAM (quadrature amplitude modulation with unevenconstellation) transmitter and receiver provided by an embodiment of theapplication;

FIG. 2 is a block diagram of a UASK/UQAM transmitter and receiverprovided by an embodiment of the application featuring a parameteradaptor;

FIG. 3 is a block diagram of a UASK/UQAM transmitter and receiverprovided by an embodiment of the application in which multiple bitstreams for multiple users are combined;

FIG. 4 is a block diagram of a UASK/UQAM transmitter and receiverprovided by an embodiment of the application in which multiple bitstreams for multiple users are combined, and also featuring a parameteradaptor;

FIG. 5 is a pictorial representation of a constellation of 4-ASK withuneven distances;

FIG. 6 is a pictorial representation of a constellation of 16-QAM withuneven distances;

FIG. 7 is a pictorial representation of a constellation of 8-ASK withuneven distances;

FIG. 8A is a block diagram of an example implementation of a 16-UQAMmodulator with a bit stream mapper implemented;

FIG. 8B is a block diagram of an example implementation of a 16-UQAMmodulator without a bit stream mapper implemented;

FIG. 9A is a block diagram of a receiver and demodulator for processingsignals generated by the modulator of FIG. 8A;

FIG. 9B is a block diagram of a receiver and demodulator for processingsignals generated by the modulator of FIG. 8B;

FIG. 10 contains plots of the BER vs. E_(b)/N_(o) of 4-UASK in an AWGN(Additive White Gaussian Noise) channel (μ=1.0, 0.7 and 0.4);

FIG. 11 contains plots of the BER vs. E_(b)/N_(o) of 4-UASK in aRayleigh fading channel (μ=1.0, 0.7 and 0.4);

FIG. 12 is a block diagram of a transmitter and receivers in which4-UASK is employed for the data transmission for two users;

FIG. 13 is a schematic diagram showing the application of multi-userUASK or UQAM to GSM (Global System for Mobile Communication);

FIG. 14 is a schematic diagram of a transmitter showing the applicationof 16-UQAM for four users, in which training sequences are used toencode the constellation properties and to assign bits to a particularuser;

FIG. 15 is a block diagram of a system featuring a codec, a channelencoder, and interleaver, a bit puncturer and bit stream mapper followedby a UASK or UQAM modulator;

FIG. 16 is a flowchart of a method of using an uneven constellation in aspeech encoder application;

FIG. 17 is a block diagram of another mobile device.

DETAILED DESCRIPTION

A broad aspect of the application provides a transmitter comprising: aUASK (amplitude shift keying with uneven distance) modulator or UQAM(quadrature amplitude modulation with uneven distance) modulator thatgenerates symbols from input bits for multiple receivers such that atleast some of the symbols generated by the UASK modulator or UQAMmodulator are multi-user symbols that contain bits for multiplereceivers.

A broad aspect of the application provides a method comprising:generating UASK (amplitude shift keying with uneven distance) symbols orUQAM (quadrature amplitude modulation with uneven distance) symbols frominput bits destined for multiple receivers such that at least some ofthe symbols generated are multi-user symbols that contain bits formultiple receivers; transmitting a signal containing the symbols.

Another broad aspect provides a receiver comprising: a UASK (unevenamplitude shift keying) demodulator or UQAM (uneven quadrature amplitudemodulation) demodulator that produces bits from received symbols,wherein at least some of the symbols are multi-user symbols that containbits of multiple receivers, the receiver being further configured toextract bits that are for that receiver.

Another broad aspect provides a method in a receiver comprising:receiving a signal containing symbols, at least some of the symbolsbeing multi-user UASK symbols that contain bits for multiple receivers,or at least some of the symbols being multi-user UQAM symbols thatcontain bits of multiple receivers; performing UASK (uneven amplitudeshift keying) demodulation or performing UQAM (uneven quadratureamplitude modulation) demodulation to produce bits from the symbols;extracting bits that are for that receiver.

It should be understood at the outset that although illustrativeimplementations of one or more embodiments of the present disclosure areprovided below, the disclosed systems and/or methods may be implementedusing any number of techniques, whether currently known or in existence.The disclosure should in no way be limited to the illustrativeimplementations, drawings, and techniques illustrated below, includingthe exemplary designs and implementations illustrated and describedherein, but may be modified within the scope of the appended claimsalong with their full scope of equivalents.

Systems and methods that employ ASK and QAM modulation schemes withuneven constellations, that is, the distances between two neighboringsignal points (referred to as neighboring distance hereafter) in theconstellations are not equal, are provided. These modulation schemeswill be referred to as UASK (amplitude shift keying with unevenconstellation) and UQAM (quadrature amplitude modulation with unevenconstellation) respectively. A UASK constellation is an ASKconstellation in which the distances between neighboring symbols in theconstellation are not all equal. Similarly, with a UQAM constellation,the distance between neighboring symbols along the real axis are not allequal and/or the distance between neighboring symbols along theimaginary axis are not all equal. In some embodiments, this is employedto provide controllable bit-error rate (BER) performance, in some casesadaptively controllable, for each bit among the k bits.

Other embodiments provide one or more computer readable media havingcomputer executable instructions stored thereon for executing, orcoordinating the execution of one or more of the methods summarizedabove, or detailed below.

Referring now to FIG. 1, a first embodiment of the application will nowbe described. A transmitter is generally indicated at 300 and is shownto include a UASK or UQAM modulator 304 and an antenna 306. Typically,the transmitter would include either a UASK modulator, or a UQAMmodulator, but the Figure shows both in the interest of brevity. TheUASK or UQAM modulator 304 receives bits 302 to be mapped to symbols bythe UASK or UQAM modulator. Details of UASK and UQAM modulation areprovided below. For the embodiment of FIG. 1, bits 302 may include bitswhich are for one or multiple users to receive depending on a givenimplementation or application. The UASK or UQAM modulator 304 uses atleast one adaptation parameter μ 320 indicative of what constellation touse, for example reflective of unevenness in the constellation. Moregenerally, the modulator simply needs to know which symbol constellationto use. For constellations of larger size, there may be multiple suchadaptation parameters, in order to provide multiple differentneighboring distances between constellation points. In some embodiments,the uneven constellation used with the embodiment of FIG. 1 is fixed. Inother embodiments, the constellation is changed adaptively or changed ina predetermined manner.

The receiver is generally indicated at 310, and includes a receiveantenna 312 and UASK or UQAM demodulator 314 which produces output 316.The UASK or UQAM demodulator 314 performs UASK or UQAM demodulation.Details of UASK and UQAM demodulation are provided below. The μ value(s)322 used in the UASK and UQAM demodulation are the same as those usedfor modulation, are used for demodulation. More generally, the receiverneeds to know somehow what the symbol constellation is. In the eventbits 302 included bits for multiple users, there would be multipleinstances of the receiver 310, one for each user. Each user may bededicated to receive all or a part of the bits.

Referring now to FIG. 2, a second embodiment of the application will nowbe described. A transmitter is generally indicated at 340 and is shownto include a UASK or UQAM modulator 344 and an antenna 346. The UASK orUQAM modulator 344 receives bits 342 to be mapped to symbols by the UASKor UQAM modulator. For the embodiment of FIG. 2, bits 342 may includebits which are for one or multiple users depending on a givenimplementation or application. Also shown is a parameter adaptor 348that adaptively determines a constellation to be used by the UASKmodulator or the UQAM modulator. In the illustrated example, thisinvolves determining at least one parameter μ indicative of whichconstellation to use, for example one or more parameters reflective ofunevenness in the constellation, and provides this at 350 to the UASK orUQAM modulator 344. For the constellations of large size, there may bemultiple such parameters if multiple different neighboring distances areto be provided. The parameter adaptor 348 takes into account at leastone adaptation input 352. Adaptation input(s) are application specific.In some embodiments, they are reflective (directly or indirectly) of adesired level of BER disparity between different bits (i.e., the bits atdifferent bit positions); in some embodiments, they are reflective(directly or indirectly) of different channel conditions to beexperienced by multiple receivers dedicated to receive different bits.In some embodiments, they are reflective (directly or indirectly) of thepossibly different noise and interference suppression capabilities ofthe targeted receivers. Specific examples of adaptation inputs includerequired SNR (signal to noise ratio) or SINR (signal-to-interferenceplus noise ratio) for a targeted service quality, or measured SNR orSINR. More examples of adaptation inputs include RSSI (received signalstrength indication), BER, BLER (block error rate), Mean BEP (bit errorrate probability), CV BEP (coefficient of variance for BEP), FER (frameerror rate), advanced receiver Capabilities (for example DARP Phase I,DARP Phase II), MCS (modulation and coding scheme), etc. The parameteradaptor 348 determines the constellation to use, and also may change theconstellation used in a way that may, for example, be periodic oraperiodic. The UASK or UQAM modulator 344 uses the parameter(s) μ to setthe constellation used for modulation. In some embodiments, thetransmitter is configured to transmit at least one parameter reflectiveof unevenness in the constellation over a communication link, forexample wireless or wire-line, for use by at least one receiver inperforming demodulation.

The receiver is generally indicated at 360, and includes a receiveantenna 361 and UASK or UQAM demodulator 362 which produces output 366.The UASK or UQAM demodulator 362 performs UASK or UQAM demodulation,optionally taking into account one or more of the parameter(s) μ showninput at 364. In the event bits 342 included bits for multiple users,there would be multiple instances of the receiver 360, one for eachuser. Each user may be dedicated to receive all or a part of the bits.For multiple user embodiments, as detailed below, not every receivernecessarily will need to be aware of any of the parameter(s) μ. Forreceivers that do need to be aware, they can learn of the parameter(s)by, for example, receiving signaling that indicates the parameter(s), byanalyzing the received signal to estimate the parameter(s). It is alsopossible that the parameter(s) μ have been predetermined and hence thereceiver will know the parameter(s) μ and when they are used. Moregenerally, the receivers need to be aware of what constellation to usein performing demodulation.

Referring now to FIG. 3, a third embodiment of the application will nowbe described. A transmitter is generally indicated at 370 and is shownto include a UASK or UQAM modulator 374 and an antenna 376. The UASK orUQAM modulator 374 receives bits 372 that include bits from N differentstreams, for N different users, to be mapped to symbols by the UASK orUQAM modulator, where N≧2. Each symbol produced by the UASK or UQAMmodulator may contain one or more bits for each of the users, or for asubset of the users. More generally, at least some of the symbolscontain bits for multiple users. The UASK or UQAM modulator 374 uses atleast one parameter μ 375 reflective of unevenness in the constellation.More generally, the modulator needs to know which symbol constellationto use. For constellations of larger size, there may be multiple suchparameters if multiple different neighboring distances are to beprovided. In some embodiments, the transmitter performs a mapping whichmay be static or dynamic of the input bits 372 for the multiple users tobit positions for the purpose of UASK or UQAM modulation. Theillustrated bit stream mapper 373 is one example of where this mighttake place.

A set of receivers includes a receiver for each of the N users,specifically, user 1 receiver 380, user 2 receiver 381 and so on throughto user N receiver 383. Only receiver 380 will be described in detail.The receiver includes a receive antenna 382, UASK or UQAM demodulator384 which produces output 386. The UASK or UQAM demodulator 384 performsUASK or UQAM demodulation. The μ value(s) 385 which are the same asthose used in the modulation are used by the receiver for demodulation.More generally, the receiver needs to know somehow what the symbolconstellation is. In embodiments in which the transmitter performed amapping which may be static or dynamic of the input bits 372 for themultiple users to bit positions for the purpose of UASK or UQAMmodulation, the receiver needs to be aware of the mapping in order toextract the bits for that receiver. In some embodiments, the receiverincludes a bit stream demapper 388 for this purpose which simplyextracts the bits that are for that receiver. In the illustratedexample, the bit stream mapper 388 makes use of one or more parameters Lindicative of the position of the bits for that receiver. In someembodiments, these are received over the air. A specific example isdetailed below in which a parameter L is conveyed though the use oftraining sequences.

In some embodiments, the uneven constellation used with the embodimentof FIG. 3 is fixed. In other embodiments, the constellation is changedadaptively or in a predetermined manner.

Referring now to FIG. 4, a fourth embodiment of the application will nowbe described. A transmitter is generally indicated at 390 and is shownto include a UASK or UQAM modulator 394 and an antenna 396. The UASK orUQAM modulator 394 receives bits 392 to be mapped to symbols by the UASKor UQAM modulator that include bits from N different streams, for Ndifferent users, where N≧2. Each symbol produced by the UASK or UQAMmodulator may contain one or more bits for each of the users, or for asubset of the users. More generally, at least some of the symbolscontain bits for multiple users. Also shown is a parameter adaptor 398that adaptively determines a constellation to be used by the UASKmodulator or the UQAM modulator. This may for example involvedetermining at least one parameter μ indicative of what constellation touse, for example reflective of unevenness in the constellation andprovides this at 400 to the UASK or UQAM modulator 394. Forconstellations of larger size, there may be multiple such parameters ifmultiple different neighboring distances are to be provided. Theparameter adaptor 398 takes into account at least one adaptation input402. The adaptation inputs that are used by the parameter adaptor mayvary depending on the application. In some embodiments, they arereflective (directly or indirectly) of different channel conditions tobe experienced by multiple receivers dedicated to receive the differentbits. In some embodiments, they are reflective (directly or indirectly)of the possibly different noise and interference suppressioncapabilities of the targeted receivers. In some embodiments, they arereflective (directly or indirectly) of the possibly different noise andinterference suppression capabilities of the targeted receivers.Specific examples of adaptation inputs include required SNR (signal tonoise ratio) or SINR (signal-to-interference plus noise ratio) for atargeted service quality, or measured SNR or SINR. More general examplesof adaptation inputs could include RSSI (received signal strengthindication), BER, BLER (block error rate), Mean BEP (bit error rateprobability), CV BEP (coefficient of variance for BEP), FER (frame errorrate), advanced receiver Capabilities (for example DARP Phase I, DARPPhase II), MCS (modulation and coding scheme), etc. The parameteradaptor 348 determines the constellation to use, and may change theconstellation used in a way that may, for example, be periodic oraperiodic. The UASK or UQAM modulator 394 uses the at least oneparameter μ to set the constellation used for modulation. In someembodiments, the transmitter is configured to transmit the at least oneparameter reflective of unevenness in the constellation over acommunication link, for example wireless or wire-line, for use by atleast one receiver in performing demodulation. In some embodiments, thetransmitter performs a mapping which may be static or dynamic of theinput bits 392 for the multiple users to bit positions for the purposeof UASK or UQAM modulation. The illustrated bit stream mapper 393 is oneexample of where this might take place.

A set of receivers includes a receiver for each of the N users,specifically, user 1 receiver 410, user 2 receiver 411 and so on throughto user N receiver 413. Only receiver 410 will be described in detail.Receiver 410 includes a receive antenna 412, UASK or UQAM demodulator414 which produces output 416. The UASK or UQAM demodulator 414 performsdemodulation, optionally taking into account one or more of theparameter(s) μ as indicated at 418. For each symbol, each user may bededicated to receive none, all, or a part of the demodulated bits.Receivers can learn of the parameter(s) μ by receiving signaling thatindicates the parameter(s), or analyzing the received signal to estimatethe parameter(s). It is also possible that the parameter(s) μ have beenpredetermined and hence the receiver will know the parameter(s) μ andwhen they are used. In embodiments in which the transmitter performed amapping which may be static or dynamic of the input bits 392 for themultiple users to bit positions for the purpose of UASK or UQAMmodulation, the receiver needs to be aware of the mapping in order toextract the bits for that receiver. In some embodiments, the receiverincludes a bit stream demapper 420 for this purpose which simplyextracts the bits that are for that receiver. In the illustratedexample, the bit stream mapper 388 makes use of one or more parameters Lindicative of the position of the bits for that receiver. In someembodiments, these are received over the air. A specific example isdetailed below in which a parameter L is conveyed though the use oftraining sequences.

Note that the transmitters of FIGS. 1, 2, 3 and 4 may include many othercomponents that have not been shown. A non-exhaustive set of examples ofwhat may be included is source encoders, channel encoders, digital toanalog converters, filters, frequency up-converter(s), RF amplifiers.Furthermore, while the transmitters are each shown to have a singleantenna, it should be understood that multiple antenna implementationsare possible as well in the transmitter. While all of the embodimentdescribed assume a wireless channel, more generally, any communicationschannel is contemplated. For example, the communications channel may bea wired connection in which case, a transmitter may generate an RFsignal for transmission without an antenna, by way of the wiredconnection. In such embodiments, neither the transmitter nor thereceiver require antennas.

Some embodiments further include the above-described bit stream mapperbetween the input bit stream(s) and the modulator, that maps input bitsto bit positions. In some embodiments, the bit stream mapper works inconnection with the constellation selection process and takes intoaccount the adaptation inputs. Specific examples of embodiments thatinclude bit stream mappers are described below. For example, for theUASK case, each symbol is determined by two bits, a strong bit and aweak bit. The strong bit is transmitted with relatively stronger errorimmunity than the weak bit. If the data for a first and second user isto be carried by the two bits, the bit stream mapper decides whichuser's data should be transmitted as the strong bit or weak bit. Thiswill result in the assignment of different BER performances to the firstand second users, or can be used to achieve BER parity between the twousers where one user experiences different channel propagationconditions, more noise and or interference, or has a less advancedreceiver capability for suppressing noise and or interference. Thefunction of the bit stream mapper is not limited to the multiple usercase. Bit stream mapping may be performed adaptively or in a fixedmanner. In the event adaptation is employed, adaptation inputs that arethe same or similar to those described for the adaptation of the symbolconstellation may be employed. The adaptation inputs are used by the bitstream mapper to determine the relative assignment of input bit strengthrequirements to symbol constellation point strength.

Some single user applications also may benefit from bit stream mapping.In that case bits for the single user are selectively mapped to bitpositions so as to control BER of the various bits. A specific exampleof where this is applied to the output of a codec is described in detailbelow.

The BER achieved by a given receiver is a function of more than just thesymbol constellation used at the transmitter. It is also a function ofthe channel conditions at the times of transmission between thetransmitter and the receiver. It is also a function of the capabilitiesof the receiver in terms of its ability to suppress noise andinterference. These factors can differ between a set of receivers whoare to each receive one or more bits of a transmitted UASK or UQAMsymbol.

In some embodiments, the parameter adaptor is configured to determinethe constellation by taking into account a target BER performance fordifferent bit positions of the input bits. Target BER performance isused in a very general sense, and can include specific targets orranges, or relative targets or ranges to name a few specific examples,or simply relative BER performances of the different bit positions.

For applications with a single receiver, this may involve determiningthe constellation by taking into account a target differentiated BERperformance for different bit positions of the input bits that are forreceipt by a common receiver, and then subsequently mapping the bits tothe specific constellation positions using the bit stream mapper.

In some embodiments, the parameter adaptor is configured to determine aconstellation to be used by the UASK modulator or the UQAM modulator bytaking into account a target BER performance for different bit positionsof the input bits as received by different receivers. Again, this mayinvolve taking into account the target BER, channel conditions, and/orreceiver capabilities to name a few examples. The bit stream mapper isthen used to map the input bits destined for different receivers ontothe symbol constellation points in a manner which adaptively changesbased on the changing targeted BER performance, changing transmissionchannel conditions, or any other dynamic characteristic.

The receivers of FIGS. 1, 2, 3 and 4 may include other components thathave not been shown. A non-exhaustive set of examples of what may beincluded is RF front ends, frequency down-converter(s), analog todigital converters, hard or soft bit decider(s), channel decoders,equalizers, source decoders. Furthermore, while the receivers are eachshown to have a single antenna, it should be understood that multipleantenna receiver implementations are possible as well, as areimplementations where the RF input is delivered in a conducted mannerinstead of a radiated manner. In some embodiments, the receiver has aparameter estimator or detector (not shown) that estimates or otherwisedetermines the μ value(s) of the UQAM or UASK constellation by examiningthe received symbol. More generally, the receiver has some mechanism todetermine the constellation that was used at the transmitter. Of course,this would not be necessary if the constellation was fixed and known tothe receiver. In some embodiments, the receiver has a parameterestimator or detector (not shown) that estimates or otherwise determinesthe L value(s) indicative of which bits are for the receiver. Moregenerally, the receiver has some mechanism to determine which bits arefor the receiver. Of course, this would not be necessary if the mappingwas fixed and known to the receiver.

For some embodiments, for a given modulation type, e.g. ASK or QAM,there are a finite number of different constellations that are selectedbetween, each with different spacings of the symbol points in theconstellations, each yielding corresponding differences in BERsexperienced by the various bit positions. In such a case, the parameterindicative of unevenness of the constellation may simply be aconstellation identifier that indicates a selected one of the finitenumber of different constellations employed by the transmitter.

Quaternary Uneven Ask

Referring now to FIG. 5, shown is the constellation of quaternary unevenASK (4-UASK) provided by an aspect of the application. The horizontalaxis 18 represents the baseband signal amplitude. The constellationincludes four symbols referred to as s₁ 10, s₂ 12, s₃ 14, s₄ 16. Alsoshown in the figure generally indicated at 20 is an example ofbit-to-symbol mapping of bits b₁b₂ that follows the Gray coding rule. Itshould be understood that the bit-to-symbol mapping relationship is notunique for this and the other examples given below. In some embodimentsfor this and other examples below, any Gray code mapping can beemployed. For a Gray code mapping, two neighboring symbols in theconstellation, have bit representations (i.e. presented by b₁b₂) thatdiffer by only one bit. The distance between the two inner points s₂ 12,s₃ 14 is denoted by a positive real number, d, while the distancebetween an outer point and its neighbor (for example between s₃ 14 ands₄ 16) is denoted by μ d, where μ is a positive real number. When μ=1.0,FIG. 5 represents a regular 4-ASK constellation with equal distancebetween all neighboring points, and otherwise it represents a 4-UASKconstellation. For reasons described below, the bit denoted by b₁ willbe referred to as the strong bit, and the bit denoted by b₂ will bereferred to as the weak bit. The average symbol energy is

$\begin{matrix}{{E_{s} = {{\frac{1}{2}\left\lbrack {\left( {\frac{d}{2} + {\mu \; d}} \right)^{2} + \left( \frac{d}{2} \right)^{2}} \right\rbrack} = {{\frac{d^{2}}{8}\left\lbrack {\left( {{2\; \mu} + 1} \right)^{2} + 1} \right\rbrack}.{Thus}}}},} & (1) \\{{d = \sqrt{\frac{8E_{s}}{B(\mu)}}}{where}} & (2) \\{{B(\mu)} = {\left( {{2\; \mu} + 1} \right)^{2} + 1.}} & (3)\end{matrix}$

The average energy of each bit is E_(b)=E_(s)/k, where k=log₂(M)=2 forM=4=the signal constellation size.

In the receiver, the two bits of each symbol can be jointly orindividually detected. For example, a hard decision can be made for eachbit following the rules,

$\begin{matrix}{{\hat{b}}_{1} = \left\{ \begin{matrix}0 & {{{if}\mspace{14mu} r} > 0} \\1 & {otherwise}\end{matrix} \right.} & (4) \\{{\hat{b}}_{2} = \left\{ \begin{matrix}0 & {{{if}\mspace{14mu} {r}} < {\left( {\mu + 1} \right){d/2}}} \\1 & {otherwise}\end{matrix} \right.} & (5)\end{matrix}$

where r is the received symbol. A soft decision on each bit is alsopossible, which is often desirable when channel decoding follows. Insome other implementation examples, it is also possible to include asymbol detector which makes a decision on each symbol, and then demapthe symbol to the wanted bits.

In FIG. 5, the parameter μ is defined by the ratio of the distancebetween an outer symbol and its neighboring symbol to the distancebetween two inner symbols of the constellation. It should be apparentthat a constellation having the symbol spacings of the FIG. 5 examplecan equivalently be defined using many different parameter definitions.Furthermore, the constellation could be defined without using anyadaptation parameters at all, for example simply by providing values forthe constellation points.

16-Ary Uneven QAM

In another embodiment, the concept of 4-UASK is extended to 16-aryuneven QAM (16-UQAM) by constituting the 16-UQAM constellation with twoindependent 4-UASK constellations, one for the real part, i.e., thein-phase (I) sub-channel, and another for the imaginary part, i.e., thequadrature (Q) sub-channel. An example of this is shown in FIG. 6, wherefor each block of k=4 bits, two of them (b₁ and b₂) are mapped to thesub-channel I (indicated by horizontal axis 100), and other two bits (b₃and b₄) are mapped to the sub-channel Q (indicated by vertical axis102). By setting a proper value of μ for each sub-channel, different BERperformances of the strong bits and the weak bits can be obtained foreach sub-channel.

Note that in FIG. 6, the values of μ are denoted by μ_(i) and μ_(q) forthe sub-channel I and Q, respectively. In addition, the values of d aredenoted by d_(i) and d_(q) for the two sub-channels respectively. Ingeneral, μ_(q) is not necessarily equal to μ_(i), and, d_(q) is notnecessarily equal to d_(i). These flexibilities make it possible to letall of the four bits have different BER performances.

The parameters μ_(i), and, μ_(q) function similar to the singleparameter μ for the FIG. 5 example. More specifically, μ_(i) is theratio of the distance between an outer symbol and its neighboring symbolto the distance between the two inner symbols of the constellation inthe I dimension, while μ_(q) is the ratio of the distance between anouter symbol and its neighboring symbol to the distance between the twoinner symbols of the constellation in the Q dimension. Again, it shouldbe apparent that the constellation of FIG. 6 need not necessarily bedefined using these particular parameter definitions. Other parametersreflective of the unevenness of the constellations could be employed, orfixed constellations may be employed in which the constellation pointsare defined without reference to any parameters.

In the receiver, the four bits of each symbol can be jointly, partiallyjointly, or individually detected. For example, the real part and theimaginary part of the received complex symbol can be separated, and ahard decision can be made for each bit following the rules.

$\begin{matrix}{{\hat{b}}_{1} = \left\{ \begin{matrix}0 & {{{if}\mspace{14mu} {Re}\left\{ r \right\}} > 0} \\1 & {otherwise}\end{matrix} \right.} & (6) \\{{\hat{b}}_{2} = \left\{ \begin{matrix}0 & {{{if}\mspace{14mu} {{{Re}\left\{ r \right\}}}} < {\left( {\mu_{i} + 1} \right){d_{i}/2}}} \\1 & {otherwise}\end{matrix} \right.} & (7) \\{{\hat{b}}_{3} = \left\{ \begin{matrix}0 & {{{if}\mspace{14mu} {Im}\left\{ r \right\}} > 0} \\1 & {otherwise}\end{matrix} \right.} & (8) \\{{\hat{b}}_{4} = \left\{ \begin{matrix}0 & {{{if}\mspace{14mu} {{{Im}\left\{ r \right\}}}} < {\left( {\mu_{q} + 1} \right){d_{q}/2}}} \\1 & {otherwise}\end{matrix} \right.} & (9)\end{matrix}$

where Re{r} and Im{r} are the real part and the imaginary part of thereceived complex symbol r, respectively. Again, a soft decision can bemade for each bit, which is often desirable when channel decodingfollows. In some other implementation examples, it is also possible toinclude a symbol detector which makes a decision on each symbol, andthen de-map the symbol to the wanted bits.

Higher Order Uneven ASK and QAM

In another embodiment, the above-described concept of 4-UASK isgeneralized to higher order UASK. As an example, FIG. 7 illustrates ahigher order UASK constellation. As M=8 and k=3, each block of 3 bits,denoted by b₁, b₂ and b₃, is mapped to a 8-UASK symbol following Graycoding as generally indicated at 128. The horizontal axis 126 representsbaseband signal amplitude. The constellation includes eight symbolsreferred to as s₁ 110, s₂ 112, s₃ 114, s₄ 116, s₅ 118, s₆ 120, s₇ 122,s₈ 124. The distance between the two inner points s₄ 116, s₅ 118 isdenoted by d, while the distances between other neighboring pointsareμ_(i)d, where i=1, 2 or 3. For different choices of the values ofμ_(i), the BER performances of the 3 bits can be calculated or simulatedand thus the choice of the values of μ_(i) permit the BER performance ofthe 3 bits to be set differently. In the receiver, the three bits ofeach symbol can be jointly, or individually detected. For example, ahard decision can be made for each bit as follows,

$\begin{matrix}{{\hat{b}}_{1} = \left\{ \begin{matrix}0 & {{{if}\mspace{14mu} r} < 0} \\1 & {otherwise}\end{matrix} \right.} & (10) \\{{\hat{b}}_{2} = \left\{ \begin{matrix}0 & {{{if}\mspace{14mu} {r}} > x_{2}} \\1 & {otherwise}\end{matrix} \right.} & (11) \\{{\hat{b}}_{3} = \left\{ \begin{matrix}0 & {{{if}\mspace{14mu} x_{1}} < {r} < x_{3}} \\1 & {otherwise}\end{matrix} \right.} & (12)\end{matrix}$

where x₁, x₂ and x₃ are thresholds defined by midpoints between thesymbols. A soft decision can be made for each bit, which is oftendesirable when channel decoding follows. In some other implementationexamples, it is also possible to include a symbol detector which makes adecision on each symbol, and then de-map the symbol to the wanted bits.Higher order constellations can be defined with reference to otherparameter definitions than the above; also higher order constellationsthat are fixed may be employed.

Again, the concept of higher order UASK can be extended to higher orderUQAM as in the previously described embodiments.

IMPLEMENTATION EXAMPLES

An UASK/UQAM modulator can be implemented with any method suitable for aregular ASK/QAM modulator implementation with few changes. As anexample, FIG. 8A shows the block diagram of a possible implementation ofa 16-UQAM modulator, including a possible bit-to-symbol mappingrelationship. As will be explained in detail below, the diagram consistsof a top part 640 and a bottom part 642, representing the sub-channel Iand the sub-channel Q, respectively. Each part is a 4-UASK modulator.When the bottom part is omitted, the whole block diagram represents a4-UASK modulator. The top part 640 comprises a bit-to-symbol mapper 604,pulse-shaping filter 608, multiplier 620 and carrier source 618providing an RF cosine signal. The multiplier 620 and the carrier source618 constitute a frequency up-converter for the top part 640. The bottompart 642 comprises a bit-to-symbol mapper 610, pulse-shaping filter 614,multiplier 624 and phase shifter 622. The phase of the carrier source618 is shifted by the phase shifter 622 by 90 degrees to produce an RFsine signal 623 as input to multiplier 624. The multiplier 624 and theRF sine signal constitute a frequency up-converter for the bottom part642. The outputs of multiplier 620 and 624 are combined in adder 626 toproduce the overall output which is then forwarded for RF processing.Generally indicated at 630 is a specific example of the bit-to-symbolmapping performed in the bit-to-symbol mapper 604. Similarly, generallyindicated at 632 is a mapping performed by bit-to-symbol mapper 610. Itcan be seen that for the I and Q channels respectively, a UASK mappingis performed. Note that the parameterization of the mappings is as givenin the above example, with a single parameter pi 606 being used todefine the unevenness in the I sub-channel and a single parameter μ_(q)612 being used to define the unevenness in the Q sub-channel. Of course,as described previously, this is just one example of how to define theunevenness of the constellation. The input to the bit-to-symbol mapper604 includes bits b₁ and b₂. The input to the bit-to-symbol mapper 610includes bits b₃ and b₄. The four bits b₁, b₂, b₃ and b₄ may be for asingle receiver or for multiple receivers as described previously. Someembodiments also include a bit stream mapper. In the illustratedexample, the bit stream mapper 602 takes four input bit streamscollectively 600, a₁, a₂, a₃ and a₄, and maps these to the appropriateinputs, b₁, b₂, b₃ and b₄, of the bit-to-symbol mappers 604 and 610. Thebit stream mapper determines which input bit, among a_(i), i==1˜4, istransmitted as b₁, which input bit is transmitted as b₂, and so on.

It should be readily apparent that a transmitter design isimplementation specific, and that other components than thosespecifically shown in FIG. 8A may be employed in conjunction with a UASKor UQAM modulator.

A UASK/UQAM demodulator can be implemented with any method suitable forthe regular ASK/QAM demodulator implementation with few changes. As anexample, FIG. 9A shows a block diagram of a possible implementation fora receiver employing 4-UASK demodulation. Shown is an RF front end 650,multiplier 652 for performing down conversion, low pass filter 654, downsampler 656 and bit decider 658 which has an input to receive theparameter(s) μ indicative of the constellation to use, for examplereflective of the unevenness of the constellation. The output of the bitdecider 658 is b₁ or b₂ or both. In some other implementation examples,it is also possible to include a symbol detector which makes a decisionon each symbol, and then de-map the symbol to the wanted bits. Alsoshown is a bit stream demapper 662. In some embodiments, the bit streamdemapper 662 simply extracts bits that are for that receiver. This isappropriate for single transmitter to multiple receiver embodiments. Insome embodiments, the bit stream demapper 662 is configured to perform areverse operation upon bits of a sequencing operation that took place inthe transmitter, for example to organize transmitted bits into variousclasses. Detailed examples of this latter approach are given below. Aparameter estimator or detector 664 is provided that produces theparameter(s) μ indicative of the constellation to use. The parameterestimator or detector 664 may also provide parameter(s) indicative ofwhich bits are for the receiver, denoted by L 661, to the bit streamdemapper 662. In some embodiments, the parameter(s) μ are estimated,while in others they are detected, for example from signaling. Specificexamples of μ detection is given below. More generally, the receiverneeds to somehow determine what constellation was used at thetransmitter. In FIG. 9A, c(t) is the local carrier signal. When c(t) isthe same cosine function as that used in the top part of FIG. 8A, thebit of b₁ or b₂ or both can be recovered. Otherwise, when c(t) is thesame sine function as that used in the bottom part of FIG. 8A, the bitof b₃ or b₄ or both can be recovered. If a receiver implements tworeceiver paths, one with the cosine function, and the other with thesine function, the receiver is able to recover any combination of one ormore of b₁, b₂, b₃ and b₄. Depending on the nature of the mappingperformed in the transmitter, for such an embodiment the bit streamdemapper 662 may receive recovered bits from one or both the I and Qreceive path for the purpose of performing bit stream demapping.

It should be readily apparent that a receiver design is implementationspecific, and that other components than those specifically shown inFIG. 9A may be employed in conjunction with a UASK or UQAM modulator.

FIG. 8B is a block diagram of another implementation of a 16-UQAMmodulator. This embodiment differs from the embodiment of FIG. 8A inthat there is no bit stream mapper 602. The first bit-to-symbol mappingis performed by the bit-to-symbol mapper 604 for input bits b₁, b₂, toproduce symbols for an I sub-channel, and the second bit-to-symbolmapping is performed by the bit-to-symbol mapper 612 for input bits b₃,b₄, to produce symbols for a Q sub-channel.

FIG. 9B is a block diagram of an implementation of a receiver thatemploys 16-UQAM demodulation, corresponding with the transmitter exampleof FIG. 8B, differing from FIG. 9A in the absence of bit stream demapper662.

It should be readily apparent that a receiver design is implementationspecific, and that other components than those specifically shown inFIG. 9B may be employed in conjunction with a UASK or UQAM modulator.

BER Performance of 4-UASK and 16-UQAM 1) BER in AWGN Channel

It can be proven that in the AWGN channel, for 4-UASK, the BER of thestrong bit (i.e., b₁ in FIG. 5) is

$\begin{matrix}{{P_{A\; 1}\left( {\mu,\eta_{b}} \right)} = {{\frac{1}{4}\left\lbrack {{{erfc}\left( {\frac{{2\mu} + 1}{2}{A\left( {\mu,\eta_{b}} \right)}} \right)} + {{erfc}\left( {\frac{1}{2}{A\left( {\mu,\eta_{b}} \right)}} \right)}} \right\rbrack}.}} & (13)\end{matrix}$

The BER of the weak bit (i.e., b₂ in FIG. 5) is

$\begin{matrix}{{P_{A\; 2}\left( {\mu,\eta_{b}} \right)} = {{\frac{1}{4}\begin{bmatrix}{{2\; {{erfc}\left( {\frac{\mu}{2}{A\left( {\mu,\eta_{b}} \right)}} \right)}} + {{erfc}\left( {\frac{\mu + 2}{2}{A\left( {\mu,\eta_{b}} \right)}} \right)} -} \\{{erfc}\left( {\frac{{3\mu} + 2}{2}{A\left( {\mu,\eta_{b}} \right)}} \right)}\end{bmatrix}}.}} & (14)\end{matrix}$

In (13) and (14), η_(b) is the average signal-to-noise ratio (SNR) perbit, that is,

$\begin{matrix}{{\eta_{b} = {E_{b}/N_{o}}},} & (15) \\{{{{erfc}(x)} = {\frac{2}{\sqrt{\pi}}{\int_{x}^{\infty}{{\exp \left( {- t^{2}} \right)}{t}}}}},{and}} & (16) \\{{A\left( {\mu,\eta_{b}} \right)} = {4{\sqrt{\eta_{b}/{B(\mu)}}.}}} & (17)\end{matrix}$

In (15), N_(o) is the single-sided power spectrum density of the AWGN,and E_(b) is the average signal energy per bit.

2) BER in Rayleigh Fading Channel

In the fast flat Rayleigh fading channel, the instantaneoussignal-to-noise ratio fluctuates constantly, following the exponentialdistribution. By denoting the instantaneous bit SNR by λ, and theaverage bit SNR by η_(b), the probability density function (PDF) of λ is

$\begin{matrix}{{p_{\lambda} = {\frac{1}{\eta_{b}}{\exp \left( {- \frac{\lambda}{\eta_{b}}} \right)}}},{{{for}\mspace{14mu} 0} \leq \lambda \leq {\infty.}}} & (18)\end{matrix}$

Then, the error rate in a fast flat Rayleigh fading channel is

$\begin{matrix}{{P_{Ri} = {{\int_{0}^{\infty}{{P_{Ai}\left( {\mu,\lambda} \right)}p_{\lambda}{\lambda}}} = {\int_{0}^{\infty}{{P_{Ai}\left( {\mu,\lambda} \right)}\frac{1}{\eta_{b}}{\exp \left( {- \frac{\lambda}{\eta_{b}}} \right)}{\lambda}}}}},} & (19)\end{matrix}$

where P_(Ai)(μ,λ) is the bit error rate in AWGN. Substituting (13) into(19), for the 4-UASK, the BER for the strong bit is obtained as

$\begin{matrix}{{P_{R\; 1}\left( {\mu,\eta_{b}} \right)} = {\frac{1}{2} - {{\frac{1}{4}\left\lbrack {\sqrt{\frac{4\left( {{2\mu} + 1} \right)^{2}\eta_{b}}{{4\left( {{2\mu} + 1} \right)^{2}\eta_{b}} + {B(\mu)}}} + \sqrt{\frac{4\eta_{b}}{{4\eta_{b}} + {B(\mu)}}}} \right\rbrack}.}}} & (20)\end{matrix}$

By substituting (14) into (19), the BER for the weak bit is obtained as

$\begin{matrix}{{P_{R\; 2}\left( {\mu,\eta_{b}} \right)} = {\frac{1}{2} - {{\frac{1}{4}\begin{bmatrix}{{2\sqrt{\frac{8\mu^{2}\eta_{b}}{{8\mu^{2}\eta_{b}} + {2{B(\mu)}}}}} +} \\{\sqrt{\frac{8\left( {\mu + 2} \right)^{2}\eta_{b}}{{8\left( {\mu + 2} \right)^{2}\eta_{b}} + {2{B(\mu)}}}} - \sqrt{\frac{8\left( {{3\mu} + 2} \right)^{2}\eta_{b}}{{8\left( {{3\mu} + 2} \right)^{2}\eta_{b}} + {2{B(\mu)}}}}}\end{bmatrix}}.}}} & (21)\end{matrix}$

3) Numerical Results

FIG. 10 shows the BER for the strong bit and the weak bit of 4-UASK inthe AWGN channel for μ=0.4, 0.7 and 1.0, plotted according to (13) and(14). Specifically, the BER for the strong bit for μ=1.0 is indicated at30 and the BER for the weak bit for μ=1.0 is indicated at 32. The BERfor the strong bit for μ=0.7 is indicated at 34 and the BER for the weakbit for μ=0.7 is indicated at 36. The BER for the strong bit for μ=0.4is indicated at 38 and the BER for the weak bit for μ=0.4 is indicatedat 40.

FIG. 11 shows the BER for the strong bit and the weak bit of 4-UASK inthe fast flat Rayleigh fading channel for μ=0.4, 0.7 and 1.0, plottedaccording to (20) and (21). Specifically, the BER for the strong bit forμ=1.0 is indicated at 60 and the BER for the weak bit for μ=1.0 isindicated at 62. The BER for the strong bit for μ=0.7 is indicated at 64and the BER for the weak bit for μ=0.7 is indicated at 66. The BER forthe strong bit for μ=0.4 is indicated at 68 and the BER for the weak bitfor μ=0.4 is indicated at 70.

Some numerical results are summarized in Table 1. It can be seen that inthe regular 4-ASK (i.e., μ=1.0), the BER performances of the strong bitand the weak bit are quite close. For instance, in the AWGN channel, thedifference between the strong bit and the weak bit is only 0.3 dB (forBER=10⁻⁴). However, in the 4-UASK, this difference increases as μdecreases. When μ=0.7, the difference becomes 3.6 dB, and when μ=0.4, itbecomes 8.4 dB. In the Rayleigh fading channel, the difference is 2.7dB, 5.4 dB and 9.8 dB for μ=1.0, 0.7 and 0.4, respectively, forBER=10⁻³.

TABLE 1 Bit-Error Rate Performance of 4-UASK Required E_(b)/N_(o) (dB)Channel μ strong bit weak bit difference AWGN (BER = 10⁻⁴) 1.0 11.9 12.20.3 0.7 10.2 13.8 3.6 0.4 8.2 16.6 8.4 Fast Flat 1.0 25.4 28.1 2.7Rayleigh fading 0.7 23.9 29.4 5.4 (BER = 10⁻³) 0.4 22.4 32.2 9.8For 16-UQAM, because of the independency between the two sub-channels,the equations (13) and (20) are valid for the BER of the strong bit ofeach sub-channel, while (14) and (21) are valid for the BER of the weakbit of the same sub-channel, where E_(b) is the average signal energy ofeach bit of the sub-channel.

Multi-User Transmission

A specific example of a transmitter and receiver that employ one of theabove-described modulation approaches will now be described withreference to FIG. 12. In this example, 4-UASK is applied to transmitcontent to two users, through either a wireless channel or a wire-linechannel. For instance, in the wireless mobile application, for thedownlink (DL) transmission from a base station (BS) to two mobilestations (MS) (that is, to two-users), the two mobile stations may belocated at different locations, and the signal reaching each receivermay experience significantly different propagation conditions. Moreoverthe relative abilities of the two receivers to suppress interference andnoise, for example with advanced receiver techniques, could bedifferent. The channel encoded data a₁ for one user is assigned to be b₁or b₂ by the bit stream mapper 142 and the channel encoded data a₂ foranother user is assigned to be the other of b₁ and b₂. The BERperformance difference between these two bits b₁ and b₂, and thereforealso between bits a₁ or a₂, can be controlled by setting a value of μ,as discussed above, taking into account the propagation condition ofeach user, the noise and interference seen by each user, and the noiseand interference suppression capabilities of each receiver.

The transmitter is generally indicated at 130. A bit stream for thefirst user, User 1, is indicated at 131, and this is processed by thesource encoder 134, the channel encoder 138. Other components such as aninterleaver, bit puncturer, and any other functions performed during thetransmit process may be included in the transmitter. Similarly, a bitstream for the second user, User 2, is indicated at 132, and this isprocessed by the source encoder 136, the channel encoder 140 and anyother functions performed during the transmit process. The output of thefirst channel is indicated at a₁ while the output of the second channelis indicated at a₂. The bit stream mapper 142 maps these to bits b₁ andb₂ as described above. The 4-UASK modulator 150 performs modulationbased on the bits received for two users. Each UASK symbol contains onebit for User 1 and one bit for User 2. The 4-UASK modulator 150 performsmodulation taking into account the value of μ received at 152. Theoutput is a symbol “s” at 156 which in the particular example isprocessed by a D/A (Digital-to-Analog) converter 158, Tx filter 160, andan RF amplifier 162 before being transmitted on transmit antenna 164. Ofcourse, the particular processing of the symbols prior to transmissionon a wireless or wireline channel is implementation specific. As inprevious embodiments, the transmitter may include additional components(e.g. a frequency up-converter), not shown.

A first receiver 170 for User 1 is shown. The receiver 170 may include areceive antenna 171 or a conducted input port, RF front-end 172, A/Dconverter 174, demodulator 176 which takes into account the parameter μinput at 177, Symbol-to-bit demapper 178 which takes into account aparameter L input at 181 indicative of which bit(s) are for thatreceiver, a bit stream demapper 179 that chooses the strong or weak bitsin the symbol constellation according to which bit is for that receiver,channel decoder 180 and optional source speech decoder 182.Symbol-to-bit demapper 178 makes a hard decision or a soft decision foreach bit. The receiver 190 for a second user, User 2, includes a receiveantenna 192 or a conducted input port, RF front-end 194, A/D converter196, demodulator 198 that performs demodulation taking into account theparameter μ at 200, a Symbol-to-bit demapper 202, which takes intoaccount parameter L input at 201 indicative of which bit(s) are for thatreceiver, a bit stream demapper 203 that chooses the strong or weak bitsin the symbol according to which bit is for that receiver, channeldecoder 204 and optional source decoder 206. Symbol-to-bit demapper 202makes a hard decision or a soft decision for each bit. Practically, if μis updated adaptively or in a predetermined manner, in some embodimentsall of the receivers are implemented to be capable of performingdemodulation taking into account a value of μ. Otherwise, if μ is fixedwithout adaptation, μ is predetermined and known by all users. It shouldbe readily apparent how to extend the example of FIG. 12 to embodimentsin which there are additional users, and embodiments in which UQAMmodulation is performed instead of UASK modulation.

GSM Embodiment

Another embodiment provides an access scheme for GSM that employstime-division multiple access (TDMA) in combination with UQAM or UASKmodulation. As shown in FIG. 13, for GSM, in the 900 MHz frequency bandfor example, the uplink and downlink are separated bands as indicated at502,504 respectively, each of which has 25 MHz bandwidth including 124channels. Carrier separation is 200 kHz. A TDMA frame is indicated at506 and consists of 8 timeslots corresponding to one carrier frequency.Each timeslot can be used to transmit a burst of symbols. In originalGSM systems, Gaussian minimum shift-keying (GMSK) modulation isemployed, each GMSK symbol carries one user bit and each timeslot maytransmit only one user's data. With M-ary ASK or M-ary QAM modulation,one symbol can transmit more bits for a single user when M≧4.Alternatively, with UASK or UQAM modulation, one timeslot can be used totransmit a burst of multi-user UASK or multi-user UQAM symbols, asindicated at 508, and each symbol transmits one or several bits for eachof multiple users in one symbol period. Alternatively, with UASK or UQAMmodulation, one timeslot can be used to transmit a burst of UASK or UQAMsymbols which are for the same receiver but are used to apply differenterror immunities (that is, different error protections) to differentbits.

More specifically, in some embodiments, each timeslot is used totransmit a burst of multi-user UASK symbols, such as 4-UASK symbols fortwo users, 8-UASK symbols for three users, or 16-UASK symbols for fourusers to name a few examples. In some embodiments, each timeslot is usedto transmit a burst of multi-user UQAM symbols, such as 16-UQAM symbolsfor four users. These embodiments at least double the peak voice or datacapacity by multiplexing at least two users simultaneously on the samephysical radio resource. When multiple mobile users are sharing the sameradio resource in a cell simultaneously, the channel quality experiencedby those users may be different due to their different physicallocations, radio environment, etc. The use of UASK or UQAM modulation tomulti-users allows the system to balance the error rate performancesamong all users and helps to reduce the overall transmitted signal powerby optimizing the relative bit error rates. In some embodiments, theconstellation is adapted with adaptive values of μ as describedpreviously in order to keep the required BER performances maintainedwhen the propagation condition varies.

Use of Training Sequences to Convey Parameter(s) Indicative ofUnevenness of the Signal Constellation and/or Bit Assignment

Another embodiment of the application provides methods and apparatus forthe use of training sequences to convey parameter(s) indicative ofunevenness of the signal constellation and/or bit assignment. Thesemethods may be used to convey μ as defined above, but more generally canbe used to convey any parameter(s) used to allow the receiver todetermine the constellation used. In the specific example detailedbelow, two different training sequences are associated with twodifferent bit assignments, this being particularly appropriate for the4-UASK embodiment to indicate either the first or second bit assignmentof two possible bit assignments. In embodiments with largerconstellations, additional training sequences may be associated withadditional bit assignments.

As an example, a detailed example of downlink (DL) transmission fortwo-users with 4-UASK will be described, in which the data for the userwho needs better link performance or error protection is designated asb₁, and the data for another user is designated as b₂. The BERperformances of these two bits can be controlled by setting a propervalue of μ, as discussed above, according to the propagation conditionsand the radio receiver capabilities of each user.

A specific method of signaling μ and bit assignment will now bedescribed for the 4-UASK embodiment that is appropriate for the GSMvoice channel, although it may find wider application.

1) Frame Structure of GSM Voice Channel

In GSM, the transmitted data sequence is organized into bursts. Eachburst occupies a time slot of 15/26 ms. Each normal burst contains asequence of 58 message bits, a training sequence code (TSC) of 26 bits,and another sequence of 58 message bits, 6 tail bits and 8.25 guardperiod bits. The TSC is used in the receiver for channel estimation andother functions. According to an embodiment of the application, it isalso used by the transmitter to signal μ and by the receiver to estimateμ. According to an embodiment of the application where a bit stream formultiple users is sent to multiple receivers, the TSC is also used tosignal which bits are assigned to each user.

2) Conveying μ to the Receiver and Estimation of μ by the Receiver

According to an embodiment of the application, a training sequence istransmitted that has embedded within it one or more parametersindicative of the constellation, for example indicative of unevenness ofthe constellation. The above-introduced μ for 4-UASK is a specificexample.

Consider a DL transmission with 4-UASK, for two users. First, twoexample training sequences of real numbers are defined in forms ofcolumn vectors of length m=26 as

t ₁ =[h, 1, −h, 1, 1, −h, 1, −h, −1, −1, h, 1, h, h, −1, h, 1, 1, −h, 1,h, −1, 1, −h, −1, −h] ^(T),

and

t ₂ =[h, −1, h, 1, 1, h, −1, −h, −1, 1, −h, −1, −h, h, −1, h, 1, −1, h,1, h, 1, −1, −h, −1, h] ^(T).

where h=1+2μ, and the superscript ^(T) stands for matrix transpose. Thebit sequences corresponding to the real sequences t₁ and t₂ may bedenoted by τ₁ and τ₂ respectively. For each burst to be transmitted,either t₁ or t₂ is selected as the training sequence. The transmittertransmits either t₁ or t₂, in so doing, signaling a value for μ to thereceiver. As such, in this application, the value of μ is fixed for atleast the length of one data burst.

The receiver knows all candidate TSC's but does not know which TSC isselected in the transmitted burst.

Corresponding to t₁ and t₂, two sequences, {tilde over (t)}₁ and {tildeover (t)}₂ are defined, respectively, by replacing h and −h in t₁ and t₂by 1 and −1 respectively. The sequences t₁ and t₂ are properly designedsuch that ideally |t_(i){tilde over (t)}_(j)|=0, or, at least,|t_(i){tilde over (t)}_(j)|<<|t_(i){tilde over (t)}_(i)|, for j≠i. Thesequences {tilde over (t)}₁ and {tilde over (t)}₂ are pre-installed inthe receiver. For convenience, a two-column matrix, T=[{tilde over (t)}₁{tilde over (t)}₂] is defined.

Two sub vectors of t_(i) are defined, denoted by t_(μ,i), where i=1 and2. The sub vector t_(μ,i) is a part of t_(i) with all entries equal to±1 deleted. In addition, two sub vectors, {tilde over (t)}_(μ,i), aredefined, obtained by replacing h in t_(μ,i) with 1. After propagatingthrough an AWGN channel, the received TSC of each burst in the receiveris

r=t _(i) +n

where t_(i) is either t₁ or t₂, and n is a vector representing thenoise. Corresponding to the sub vector t_(μ,i), a sub vector r_(μ,i) ofr is defined.

In the receiver, the estimation of μ is performed by doing the followingcalculations.

(i) Compute

x≡[x ₁ x ₂ ]=r ^(T) ·T   (22)

where x is a row vector of two real numbers. x_(i) is the inner productof r and {tilde over (t)}_(i), i=1 and 2.(ii) Compare x₁ and x₂. If x₁>x₂, let L=1; otherwise let L=2. On thebasis of the determination of L, a conclusion is reached that thetraining sequence t_(L) is used by the transmitter.(iii) Compute

y=r _(μ,L) ^(T) ·{tilde over (t)} _(μ,L)   (23)

(iv) Compute the estimate of μ as

$\begin{matrix}{\hat{\mu} = {\frac{1}{2}\left( {{\frac{m - m_{\mu}}{m_{\mu}}\frac{y}{x_{L} - y}} - 1} \right)}} & (24)\end{matrix}$

where m=26 is the length of each TSC, and m_(μ) is the length of the subvector t_(μ,L).

Increasing the length of the training sequence may increase the accuracyof the estimate. To improve the estimation accuracy, the receivedtraining sequences of multiple bursts, for example four bursts, can beconcatenated. Then, the concatenated long sequence is used as r inequation (22) above. At the same time, assuming the four bursts uses thesame TSC, {tilde over (t)}_(i), i=1 and 2, are repeated four times toform two long sequences, and these are used to form T in (22) above.Also, the concatenated r_(μ,L) from the four bursts should be used in(23), with a long sequence obtained by repeating {tilde over (t)}_(μ,L)four times.

3) Detection of Bit Assignment

In some of the embodiments described above, a bit stream mappingoperation is performed which maps bit(s) of each receiver to bitpositions for the purpose of UQAM or UASK mapping. Each receiver needsto know which bit(s) are for that receiver. In some embodiments, one ormore parameters L indicative of which bit(s) are for a given receiverare used to convey this information. A detailed example of how thisinformation might be conveyed to the receiver is provided below. Moregenerally, the receiver simply needs to know which bits are for thatreceiver, and this information can be obtained in any manner.

For the particular case where there is a weak bit and a strong bit, inaddition to knowing μ, each receiver also needs to know which bit, thestrong bit or the weak bit, is the bit assigned to that particular user.In some embodiments, a one to one correspondence between trainingsequence and bit assignment is used to signal which bit is assigned to aparticular user. For the above example, the transmitter transmits t₁ toindicate an assignment of the first bit position b₁ to the receiver(i.e. the more reliable bit position), and transmits t₂ to indicate anassignment of the second bit position b₂ to the receiver (i.e. the lessreliable bit position). In step (ii), the receiver determines a value ofL, and this can be used as an indication of the bit assignment. In aparticular example, L=1 means the user has been assigned b₁, while L=2means the user has been assigned b₂.

FIG. 14 is a block diagram of a transmitter configured to convey bitassignment and μ using training sequences associated with 16-UQAM. Toreduce the complexity, with this embodiment in 16-UQAM, both the I and Qsub channel use the same value of μ. In the illustrated example, this isachieved by dividing four users to two non-overlapping groups, with twousers in each group. In the illustrated example, the first groupcontains “User 1” and “User 2”, and the second group contains “User 3”and “User 4”. The bit streams of the two groups are selectedalternatively in time by selector logic 900. That is, during a certaintime period, e.g., a period of several bursts, the strong bits of both Iand Q sub channels are assigned to User 1, and the weak bits of both Iand Q sub channels to User 2. Then in the next period, the strong bitsof both I and Q sub channels are assigned to User 3, and the weak bitsof both I and Q sub channels to User 4. In this way, during each period,the same μ value is used for both I and Q sub channels. The mapping ofthe users within a group to either the strong or the weak channel isdone by the bit assignment block 902, this being analogous to theabove-described bit stream mapping function. The outputs of the bitassignment block 902 include strong bits and weak bits. Serial toparallel converter 904 produces a parallel output containing two strongbits b₁ and b₃. Serial to parallel converter 906 produces a paralleloutput containing two weak bits b₂ and b₄. Bits b₁, b₂, b₃ and b₄ inputto bit burst formatting 907 where a training sequence is added for eachuser. The training sequence is selected by training sequence selectionblock 912. Either training sequence τ₁ or τ₂ respectively is insertedfor each user. More generally, training sequences are used as describedabove for the purpose of conveying bit position assignment, and μ. Theoutput of the bit burst formatting 907 is mapped to 16 UQAM symbols bythe 16 U-QAM bit-to-symbol mapping 908. Parameter adaptation isindicated at 914. This involves determining what constellation to use,having regard to any of the factors mentioned previously referred tocollectively as adaptation inputs 915. In the illustrated example, thisinvolves producing the parameter μ which is used by the bit assignmentblock 902, the 16-UQAM bit-to-symbol mapping 908 and the trainingsequence selection 912. Also shown at the output is a shaping filter 916and power control block 918. In the illustrated example, the parameteradaptation 914 also has some control over the operation of the powercontrol 918. Other components may also be included.

Codec Embodiments

The embodiments described previously provide systems and methods for theuse of uneven constellations (e.g. UQAM and UASK) to providecontrollable bit-error rate (BER) performance, in some cases adaptivelycontrollable, for each bit among the k bits of each symbol.

In another embodiment, uneven symbol constellations are employed toenable the more efficient transmission of codec bit streams which haverequirements for unequal error protection. By taking advantage of thecontrollable BER performance characteristic of the bits transmittedusing uneven constellations, the overall need for additional errorcorrection may be reduced.

Generally, the bits requiring greater error protection will be sequencedinto the strong bits of the constellation and those with less subjectiveimportance will be sequenced into the weak bits of the constellation.The bit stream mapper entity described previously is one example of afunction that could perform this.

In a first specific example, it is assumed that bits are classified inaccordance with one of the conventional implementations described (forexample; Class 1a and Class 1b bits; or Class A, B or C or somealternate classification) may be transmitted at the same expected BER.

In some embodiments, bits are first ordered in sequence of decreasingimportance at the output of the codec, for example using conventionalapproaches. The ordered bits are then reordered in such a manner thateach bit is positioned such that it gets the BER performance relative toits subjective importance.

In some embodiments, the bit stream ordering from the codec may not bein sequence of decreasing importance as per the example described above.Channel coding and interleaving functions may change the ordering of thebits, but this is in a deterministic manner so the relative positions ofthe strong and weak bits are still known. Thus the bits may bere-sequenced prior to symbol modulation in order to ensure that each bitis positioned such that it gets the BER performance relative to itssubjective importance.

In some embodiments, the ordering according to importance, and thereordering for the purpose of relative BER performance are performed ina single reordering operation at the output of the codec such that eachbit output by the codec is positioned such that it gets the BERperformance relative to its subjective importance.

In some embodiments, additional processing on the bits output by thecodec is performed prior to modulation. Specific examples include butare not limited to channel coding, interleaving, and bit puncturing. Insuch embodiments, reordering is performed at some point prior to the bitto symbol mapping by a bit stream mapper, or other similar entity so asto again result in each bit being modulated being positioned such thatit gets the BER performance relative to its subjective importance.

In a specific example of this, in some embodiments, the output of thespeech encoder is further encoded using a channel encoder (for examplebut not limited to convolutional encoders, turbo encoders, Reed Solomonencoders, Trellis encoders, etc.). In some embodiments the output of thechannel encoder is then acted on by other components such as aninterleaver and a possible bit puncturer. The sequencing of the outputbits onto the strong and weak bits of the symbol constellation is doneafter all modifications to the bit stream by the possible functions hasbeen completed. The order of the bit stream is deterministic and assuch, the relative strength of the bits is still known. There may insome cases be bits that were considered strong bits prior to channelencoding that have been convolved with bits that were considered to beweak bits prior to channel encoding, resulting in bits output from thechannel encoder that are a mix of strong and weak bits. It is possiblein this case to treat these bits as strong bits. In addition, paritybits that are added to the bit stream (such as CRC bits) could beassigned to strong bit positions in the bit to symbol mapping.

Characterization of a transmission channel to identify the mostefficient combination of bit sequencing, error protection and errorconcealment to exploit the variance in bit error rate between differentbits in an uneven constellation may be employed. This process includesthe definition of a static list of the most advantageous sequence forreordering the bits from the codec output. In some embodiments, thistakes into account a puncturing process such that puncturing bits toreduce the overall transmitted bit stream is performed such that it mapsbits to the available strong bits and weak bits in an unevenconstellation whilst minimizing the impairment to received voicequality.

In some embodiments, the constellation is adaptively adjusted so as toadaptively control the BER rates available. In some embodiments, this isdone to provide a gradual variance in the BER rate from bit to bit (orfor given groups of bits) to align with the subjective importance ofeach bit.

In some embodiments, each time the constellation is adjusted, thereceiver needs to determine the constellation used. This can be done byreceiving signaling, using the above-described training sequenceapproach to name a few specific examples.

In another embodiment, the constellation is adjusted in a predeterminedmanner, for example for a block of bits that is known to the receiver.For example, in some embodiments, the value and variance of μ (moregenerally of whatever parameters are used and/or the signalconstellation per se) is predetermined and is known at both thetransmitting and receiving station. As a consequence there is no needfor the receiving station to attempt to calculate μ and hence it can bevaried more frequently than is the case when the receiver attempts torecover μ. This technique also avoids the overhead associated withexplicit signaling of μ. This would allow the optimization of the μvalues to adapt the constellations to provide a gradual variance in theBER rate from bit to bit (or for given groups of bits) to align with thesubjective importance of each bit.

The predetermined values of μ may be stored in a look up table or othermemory at the transmitting and receiving station. Different sets ofvalues of μ may be stored for different codec types and modes. In someembodiments, Over-The-Air procedures are provided to replace and/ormodify these values of μ.

As a specific example, where 150 bits are to be transmitted,constellation C1 (with first constellation unevenness that providesassociated BERs for each of four bit positions) might be used for 50 bitpositions, constellation C2 (with second constellation unevenness thatprovides associated BERs for each of four bit positions) might be usedfor 50 bit positions, and constellation C3 (with third constellationunevenness that provides associated BERs for each of four bit positions)might be used for 50 bit positions. This results in a total of 12different BERs that are available. The 150 bits would then be mapped tothe 150 bit positions such that the BER of each bit is aligned with itssubjective importance.

In systems that make use of the technique described above, it may bepossible that the same performance provided by conventionalimplementations could be available with the use of a convolutionalencoder of a different rate that reduces the overall size of thetransmitted bit stream. Alternatively additional puncturing could reducethe overall size of the block to be transmitted. Variance of both therate of the convolutional encoder and the degree of puncturing could becombined.

Codecs such at the AMR codec used in GSM and UMTS systems support avariety of modes. In some embodiments, the value and degree of varianceof the constellation unevenness is adjusted in line with changes in themode of the codec.

The use of this technique is not limited to the conventionalimplementations seen in GSM, UMTS and other cellular systems today.Characterization of the transmission channel may identify other errorcorrection and concealment techniques that would work more effectivelyin tandem with the approach. Characterization of the importance of bitsthrough subjective analysis is just one example of how bits can beprioritized. More generally, any approach to prioritization can beemployed; the approach is not limited to speech coding.

Potential advantages of this approach include, but are not limited to,increased capacity, increased voice quality (e.g. enabling higher rateoutput from the speech codec within a fixed size channel), more robusterror performance (e.g. through additional error protection exploitingthe reduction in the overall number of bits to be transmitted), andimproved efficiency (e.g. through the adaptation of the constellationspacing in line with different codec modes).

Referring now to FIG. 15, shown is a block diagram of a system thatincludes a codec 800, UQAM or UASK modulator 810, and bit stream mapper808. Optional components include a channel encoder (such as aconvolutional encoder) 804, an interleaver 805, and a bit puncturer 806.The bit stream mapper 808 represents functionality in the system that isresponsible for mapping bits to bit positions input to the modulator 810such that stronger bit positions are used for more important bits, whileweaker bit positions are used for less important bits. The specificlocation of the bit stream mapper 808 is implementation specific, andits functionality may be integrated in with other components. It shouldbe readily apparent that a codec system design is implementationspecific, and that other components than those specifically shown inFIG. 15 may be employed in conjunction with a UASK or UQAM modulator.

In a specific example, the bit stream mapper 808 reorders bits at theoutput of the codec. The reordered bits may then be subject to furthermanipulation, such as by the illustrated channel encoder and bitpuncturer. In this case, the bit stream mapper 808 accounts for whereeach bit will end up at the input to the modulator in performing itsreordering. In another example, the bit stream mapper 808 reorders bitsat the input to the modulator 810.

Referring now to FIG. 16, shown is a flowchart of a method provided byan aspect of the application. The method begins with generating a codecoutput at block 16-1. The method continues in block 16-2 with mappingbits of the codec output. In block 16-3 the bits are then used tomodulate an uneven constellation. The sequencing of the bits in block16-2 is such that such stronger bit positions of the unevenconstellation are used for more important bits, while weaker bitpositions of the constellation are used for less important bits.

The above-described techniques can be easily applied to other modulationand coding schemes that may inherently or adaptively provide unequal biterror protection. Examples of possible other modulation schemes includebut are not limited to BPSK, 8 PSK, 32 QAM etc.

Another Mobile Device

Referring now to FIG. 17, shown is a block diagram of a mobilecommunication device 700 that may implement mobile device relatedmethods described herein. It is to be understood that the mobile device700 is shown with very specific details for example purposes only.

A processing device (a microprocessor 728) is shown schematically ascoupled between a keyboard 714 and a display 726. The microprocessor 728controls operation of the display 726, as well as overall operation ofthe mobile device 700, in response to actuation of keys on the keyboard714 by a user.

The mobile device 700 has a housing that may be elongated vertically, ormay take on other sizes and shapes (including clamshell housingstructures). The keyboard 714 may include a mode selection key, or otherhardware or software for switching between text entry and telephonyentry.

In addition to the microprocessor 728, other parts of the mobile device700 are shown schematically. These include: a communications subsystem770; a short-range communications subsystem 702; the keyboard 714 andthe display 726, along with other input/output devices including a setof LEDS 704, a set of auxiliary I/O devices 706, a serial port 708, aspeaker 711 and a microphone 712; as well as memory devices including aflash memory 716 and a Random Access Memory (RAM) 718; and various otherdevice subsystems 720. The mobile device 700 may have a battery 721 topower the active elements of the mobile device 700. The mobile device700 is in some embodiments a two-way radio frequency (RF) communicationdevice having voice and data communication capabilities. In addition,the mobile device 700 in some embodiments has the capability tocommunicate with other computer systems via the Internet.

Operating system software executed by the microprocessor 728 is in someembodiments stored in a persistent store, such as the flash memory 716,but may be stored in other types of memory devices, such as a read onlymemory (ROM) or similar storage element. In addition, system software,specific device applications, or parts thereof, may be temporarilyloaded into a volatile store, such as the RAM 718. In some embodiments,one or more parameters representative of unevenness in the signalconstellation are stored in the non-volatile memory or in a volatilestore. Communication signals received by the mobile device 700 may alsobe stored to the RAM 718.

The microprocessor 728, in addition to its operating system functions,enables execution of software applications on the mobile device 700. Apredetermined set of software applications that control basic deviceoperations, such as a voice communications module 730A and a datacommunications module 730B, may be installed on the mobile device 700during manufacture. In addition, a personal information manager (PIM)application module 730C may also be installed on the mobile device 700during manufacture. The PIM application is in some embodiments capableof organizing and managing data items, such as e-mail, calendar events,voice mails, appointments, and task items. The PIM application is alsoin some embodiments capable of sending and receiving data items via awireless network 710. In some embodiments, the data items managed by thePIM application are seamlessly integrated, synchronized and updated viathe wireless network 710 with the device user's corresponding data itemsstored or associated with a host computer system. As well, additionalsoftware modules, illustrated as other software module 730N, may beinstalled during manufacture.

Communication functions, including data and voice communications, areperformed through the communication subsystem 770, and possibly throughthe short-range communications subsystem 702. The communicationsubsystem 770 includes a receiver 750, a transmitter 752 and one or moreantennas, illustrated as a receive antenna 754 and a transmit antenna756. In addition, the communication subsystem 770 also includes aprocessing module, such as a digital signal processor (DSP) 758, andlocal oscillators (LOs) 760. The specific design and implementation ofthe communication subsystem 770 is dependent upon the communicationnetwork in which the mobile device 700 is intended to operate. Forexample, the communication subsystem 770 of the mobile device 700 may bedesigned to operate with the Mobitex™, DataTAC™ or General Packet RadioService (GPRS) mobile data communication networks and also designed tooperate with any of a variety of voice communication networks, such asAdvanced Mobile Phone Service (AMPS), Time Division Multiple Access(TDMA), Code Division Multiple Access (CDMA), Personal CommunicationsService (PCS), Global System for Mobile Communications (GSM), etc. Othertypes of data and voice networks, both separate and integrated, may alsobe utilized with the mobile device 700. The particular devices underconsideration here are multi-mode mobile devices, and as such theyinclude hardware and/or software for implementing at least two RATs.More specifically, in a particular example, there would be a respectivecommunication subsystem 770 for each RAT implemented by the device.

Network access may vary depending upon the type of communication system.For example, in the Mobitex™ and DataTAC™ networks, mobile devices areregistered on the network using a unique Personal Identification Number(PIN) associated with each device. In GPRS networks, however, networkaccess is typically associated with a subscriber or user of a device. AGPRS device therefore typically has a subscriber identity module,commonly referred to as a Subscriber Identity Module (SIM) card, inorder to operate on a GPRS network.

When network registration or activation procedures have been completed,the mobile device 700 may send and receive communication signals overthe communication network 710. Signals received from the communicationnetwork 710 by the receive antenna 754 are routed to the receiver 750,which provides for signal amplification, frequency down conversion,filtering, channel selection, etc., and may also provide analog todigital conversion. Analog-to-digital conversion of the received signalallows the DSP 758 to perform more complex communication functions, suchas demodulation and decoding. In a similar manner, signals to betransmitted to the network 710 are processed (e.g., modulated andencoded) by the DSP 758 and are then provided to the transmitter 752 fordigital to analog conversion, frequency up conversion, filtering,amplification and transmission to the communication network 710 (ornetworks) via the transmit antenna 756.

In addition to processing communication signals, the DSP 758 providesfor control of the receiver 750 and the transmitter 752. For example,gains applied to communication signals in the receiver 750 and thetransmitter 752 may be adaptively controlled through automatic gaincontrol algorithms implemented in the DSP 758.

In a data communication mode, a received signal, such as a text messageor web page download, is processed by the communication subsystem 770and is input to the microprocessor 728. The received signal is thenfurther processed by the microprocessor 728 for an output to the display726, or alternatively to some other auxiliary I/O devices 706. A deviceuser may also compose data items, such as e-mail messages, using thekeyboard 714 and/or some other auxiliary I/O device 706, such as atouchpad, a rocker switch, a thumb-wheel, or some other type of inputdevice. The composed data items may then be transmitted over thecommunication network 710 via the communication subsystem 770.

In a voice communication mode, overall operation of the device issubstantially similar to the data communication mode, except thatreceived signals are output to a speaker 711, and signals fortransmission are generated by a microphone 712. Alternative voice oraudio I/O subsystems, such as a voice message recording subsystem, mayalso be implemented on the mobile device 700. In addition, the display716 may also be utilized in voice communication mode, for example, todisplay the identity of a calling party, the duration of a voice call,or other voice call related information.

The short-range communications subsystem 702 enables communicationbetween the mobile device 700 and other proximate systems or devices,which need not necessarily be similar devices. For example, theshort-range communications subsystem may include an infrared device andassociated circuits and components, or a Bluetooth™ communication moduleto provide for communication with similarly-enabled systems and devices.

Numerous modifications and variations are possible in light of the aboveteachings. It is therefore to be understood that within the scope of theappended claims, embodiments may be practiced otherwise than asspecifically described herein.

1. A transmitter comprising: a UASK (amplitude shift keying with unevendistance) modulator or UQAM (quadrature amplitude modulation with unevendistance) modulator that generates symbols from input bits for multiplereceivers such that at least some of the symbols generated by the UASKmodulator or UQAM modulator are multi-user symbols that contain bits formultiple receivers.
 2. The transmitter of claim 1 wherein the UASKmodulator or UQAM modulator employs an M-ary symbol constellation, andeach symbol produced by the UASK modulator or UQAM modulator contains abit for each of N receivers where M=2^(N), where N is an integer >=2. 3.The transmitter of claim 2 further comprising: for each user, arespective channel encoder; wherein the bit for each user is a channelencoded bit.
 4. The transmitter of claim 1 further comprising: aparameter adaptor that determines a constellation to be used by the UASKmodulator or the UQAM modulator.
 5. The transmitter of claim 4 furthercomprising: the parameter adaptor determines the constellation to beused by the UASK modulator or the UQAM modulator by determining at leastone parameter reflective of unevenness in the constellation used by theUASK modulator or the UQAM modulator.
 6. The transmitter of claim 4wherein the parameter adaptor is configured to determine theconstellation taking into account at least one adaptation input.
 7. Thetransmitter of claim 6 wherein the at least one adaptation inputcomprises at least one of: required SNR (signal to noise ratio) or SINR(signal-to-interference plus noise ratio) for a targeted servicequality, measured SNR or SINR, RSSI (received signal strengthindication), BER, BLER (block error rate), Mean BEP (bit error rateprobability), CV BEP (coefficient of variance for BEP), FER (frame errorrate), advanced receiver Capabilities (for example DARP Phase I, DARPPhase II), MCS (modulation and coding scheme).
 8. The transmitter ofclaim 4 wherein: the parameter adaptor is configured to determine theconstellation by taking into account a target BER performance fordifferent bit positions of the input bits as received by differentreceivers.
 9. The transmitter of claim 1 further configured to transmitan indication of the constellation used by the UASK modulator or theUQAM modulator.
 10. The transmitter of claim 1 further comprising: a bitstream mapper that maps bits for the multiple receivers to bit positionsfor the purpose of bit-to-symbol mapping; the transmitter furtherconfigured to transmit signaling indicative of which bit position(s) isfor which receiver.
 11. The transmitter of claim 1 comprising: a GSM(Global System for Mobile Communication) framer that produces GSM framescontaining TDMA (time division multiple access) slots; wherein for atleast some of the slots, the slots contain multi-user UASK symbols ormulti-user UQAM symbols.
 12. A method comprising: generating UASK(amplitude shift keying with uneven distance) symbols or UQAM(quadrature amplitude modulation with uneven distance) symbols frominput bits destined for multiple receivers such that at least some ofthe symbols generated are multi-user symbols that contain bits formultiple receivers; transmitting a signal containing the symbols. 13.The method of claim 12 wherein generating comprises employing an M-arysymbol constellation, and each symbol produced by the UASK modulator orUQAM modulator contains a bit for each of N receivers where M=2^(N),where N is an integer >=2.
 14. The method of claim 12 furthercomprising: performing respective channel encoding of the bits for eachreceiver prior to bit stream mapping or bit to symbol mapping.
 15. Themethod of claim 12 further comprising: determining a constellation to beused by the UASK modulator or the UQAM modulator.
 16. The method ofclaim 15 wherein: determining a constellation to be used by the UASKmodulator or the UQAM modulator comprises determining at least oneparameter reflective of unevenness in the constellation used by the UASKmodulator or the UQAM modulator.
 17. The method of claim 15 wherein:determining a constellation to be used by the UASK modulator or the UQAMmodulator comprises taking into account at least one adaptation input.18. The method of claim 15 wherein: determining a constellation to beused by the UASK modulator or the UQAM modulator comprises taking intoaccount a target BER performance for different bit positions of theinput bits as received by different receivers.
 19. The method of claim12 further comprising mapping bits for the multiple users to bitpositions for the purpose of bit-to-symbol mapping.
 20. The method ofclaim 12 further comprising: transmitting signaling indicative of theconstellation used by the UASK modulator or the UQAM modulator.
 21. Themethod of claim 20 wherein transmitting signaling indicative of theconstellation used by the UASK modulator or the UQAM modulatorcomprises: transmitting a training sequence within which is embedded atleast one parameter indicative of the constellation.
 22. The method ofclaim 20 further comprising: transmitting signaling indicative of whichbit position(s) is for which receiver.
 23. The method of claim 22wherein transmitting signaling indicative of which bit position(s) isfor which receiver comprises: for each receiver, transmitting arespective training sequence selected from a plurality of possibletraining sequences, the selection of the training sequence for eachreceiver indicating which bit position(s) are for that receiver.
 24. Areceiver comprising: a UASK (uneven amplitude shift keying) demodulatoror UQAM (uneven quadrature amplitude modulation) demodulator thatproduces bits from received symbols, wherein at least some of thesymbols are multi-user symbols that contain bits of multiple receivers,the receiver being further configured to extract bits that are for thatreceiver.
 25. The receiver of claim 24 further comprising: a bit streamde-mapper that extracts bits for that receiver.
 26. The receiver ofclaim 24 further comprising: a parameter adaptor that determines aconstellation to be used by the UASK demodulator or the UQAMdemodulator.
 27. The receiver of claim 24 further configured to extractat least one parameter reflective of unevenness in the constellationfrom the signal or elsewhere.
 28. The receiver of claim 24 wherein thereceived symbols are M-ary symbols from an M-ary symbol constellation,and each symbol contains a bit for each of N receivers where M=2^(N),where N is an integer >=2.
 29. The receiver of claim 24 furthercomprising: a channel decoder for performing channel decoding on thebits extracted for that receiver.
 30. A method in a receiver comprising:receiving a signal containing symbols, at least some of the symbolsbeing multi-user UASK symbols that contain bits for multiple receivers,or at least some of the symbols being multi-user UQAM symbols thatcontain bits of multiple receivers; performing UASK (uneven amplitudeshift keying) demodulation or performing UQAM (uneven quadratureamplitude modulation) demodulation to produce bits from the symbols;extracting bits that are for that receiver.
 31. The method of claim 30further comprising: determining a constellation to be used in performingUASK demodulation or UQAM demodulation.
 32. The method of claim 30further wherein determining a constellation to be used in performingUASK demodulation or UQAM demodulation comprises extracting at least oneparameter reflective of unevenness in the constellation from the signalor elsewhere.
 33. The method of claim 30 wherein the received symbolsare M-ary symbols from an M-ary symbol constellation, and each M-arysymbol contains a bit for each of N receivers where M=2^(N), where N isan integer >=2.
 34. The method of claim 30 further comprising:performing channel decoding on the bits extracted for that receiver. 35.The method of claim 30 further comprising: receiving signalingindicative of the constellation used by the UASK modulator or the UQAMmodulator.
 36. The method of claim 35 wherein: receiving signalingindicative of the constellation used by the UASK modulator or the UQAMmodulator comprises receiving a training sequence within which isembedded at least one parameter indicative of the constellation; themethod further comprising processing the received training sequence toextract the at least one parameter.
 37. The method of claim 30 furthercomprising: receiving signaling indicative of which bit position(s) isfor the receiver.
 38. The method of claim 37 wherein receiving signalingindicative of which bit position(s) is for the receiver comprises:receiving a training sequence selected from a plurality of possibletraining sequences, the selection of the training sequence for eachreceiver indicating which bit position(s) are for that receiver;processing the training sequence to determine which of the plurality ofpossible training sequences was received so as to thereby determinewhich bit position(s) are for that receiver.